By integration I mean political integration. I think very large states have scale problems, large democracies in particular. (Look at India or the US). You either end up with populist parties who need to appeal to the lowest common denominator of hundreds of millions of people, or technocratic elites who ignore the people. The EU has 500 million citizens from 27 ancient nations, with wildly different cultures and economies. There's no way you can fuse them into one giant country, and the inevitable outcome is fuelling nationalism and populism centred around anti-EU resentment.